A Tunisian policeman was killed in clashes with gunmen in Kasserine on the border with Algeria on Monday, a security source said, adding that military reinforcements were sent to the region.
"The clashes are continuing," he told AFP in the late afternoon, adding that two helicopters and armoured vehicles were dispatched to the area, considered a haven for smugglers.
A guard at an oil company spotted "five suspicious bearded men" near the Tunisian district of Bou Chebka, two kilometres (1.2 miles) from the Algerian border, and notified police, the source said.
The head of the police station, Anis Jlassi, was shot and killed by the gunmen and four of his men wounded, he added.
Four gunmen, probably "arms smugglers," were involved in the clashes, the security official said, but was unable to specify if they were Salafists, or hardline Muslims.
The interior ministry was not immediately available for comment.
On Saturday, a Tunisian security source reported that police had seized guns and explosives and arrested two men from the Salafist stronghold of Jendouba, north of Kasserine, in the Fernana area near the Algerian border.
In an interview published on Friday, Tunisian President Moncef Marzouki expressed concern at arms trafficking in North Africa since the fall of Libyan dictator Muammar Gaddafi.
Kadhafi's "regime accumulated weapons, and now some are in the hands not only of Islamists from Libya, but also from Algeria and Tunisia," Marzouki said in an interview with The World Today, edited by London-based think tank Chatham House.
Clashes, strikes and attacks have multiplied across Tunisia in the run up to the second anniversary of the revolution, which will be marked next Monday, plunging the country into a political impasse.
Members of Tunisia's militant Salafist movement, thought to number between 3,000 and 10,000, have been implicated in numerous acts of violence since last year's revolution.
The government, ruled by the Islamist Ennahda party, accuses Salafists of orchestrating an attack on the US embassy in Tunis and a neighbouring American school in September that left four people dead and dozens wounded.
Tunisian authorities have also arrested Salafist suspects in connection with an arson attack in October against one of the country's main Sufi shrines.